Lung carcinomas, malignant melanomas, gliomas, neuroblastomas, pheochromocytomas, colon, renal, prostate and breast carcinomas are aggressive forms of cancer, the early detection and treatment of which are of paramount importance. If left undetected or untreated for several years or even months the median survival time of patients having these types of cancers is dramatically reduced.
Of these cancers, lung cancer has lead to the highest number of fatalities. In 1992 alone, lung cancer caused about 165,000 deaths within the United States. Two major types of lung carcinomas are responsible for most of these deaths: small cell lung carcinomas (SCLC) and non-small cell lung carcinoma (NSCLC).
SCLC is a neuroendocrine tumor that secretes several peptide growth factors including bombesin/gastrin releasing peptide (BN/GRP). SCLC is responsive to chemotherapy and radiation therapy, but relapse occurs frequently, and the median survival time is only about one year.
NSCLC accounts for about 75% of all lung cancer cases and encompasses a variety carcinomas including adenocarcinomas, large cell carcinomas and squamous cell carcinomas. NSCLC tumors secrete -transforming growth factor-alpha (TGF-.alpha.) to stimulate cancer cell proliferation. NSCLC is generally treated with chemotherapy and surgical resection. However the median survival time for patients with NSCLC is only about 5 years.
Melanomas are among the most serious manifestations of skin cancer and lead to a greater number of fatalities than any other form of skin cancer. Melanomas can metastasize through the lymphatic system to regional nodes and then via the blood to secondary sites on the skin or in the liver, lungs and brain. Whereas the prognosis for superficial spreading melanomas can be quite good, there is a much poorer prognosis for nodular melanomas in which distant metastases frequently form.
Breast cancer is a major cause of death for women, and estrogen receptors ave been reported to play a major role in the development and growth of breast tumors. Deprivation of estrogen is one of the clinically effective methods for the treatment of breast cancer patients. Several growth factors such as insulin-like growth factor I (IGF-I), transforming growth factors (TGF-.alpha. and -.beta.), epidermal growth factor (EGF), and platelet-derived growth factors have been shown to be involved in the growth and progression of human breast cancer cells. Some growth factors such as TGF-.beta. act as inhibitors of tumor growth. Despite the development of numerous antiestrogen and other drugs, the clinical utility of antiestrogen is limited due to resistance by the tumor cells.
Many lives could be saved if lung carcinomas, melanomas, gliomas, neuroblastomas, pheochromocytomas, colon, prostate and renal carcinomas and breast tumors were detected and treated at an early stage. Moreover many patients are reluctant to undergo radical surgical or broad spectrum chemotherapy procedures which are frequently used to treat such cancers since these procedures can cause disfiguration or disablement.
Current techniques diagnose breast cancer by first identifying suspect tumors by single plane or 2D mammography screening. A biopsy is then required to differentiate tumors from other lesions. In the United States alone, 21 million mammographies are performed each year; 700,000 suspect tumors are biopsied and 182,000 women are diagnosed with breast cancer. This suggests that 400,000-500,000 women are subject to unnecessary biopsy each year.
Accordingly an outstanding need exists for highly selective and non-invasive procedures permitting early detection and treatment of cancer.
A variety of radiopharmaceuticals have been evaluated for diagnostic imaging. For example, Michelot, J. M. et al. (1991 J. Nucl. Med. 32:1573-1580; Meyniel G. et al. (1990 C.R. Acad. Sci. Paris 311(1):13-18; and French Patent Publication No. 2,642,972 by Morean et al. have disclose [.sup.123 I and .sup.125 I]N-(diethylaminoethyl)4-iodobenzamide (i.e. IDAB) for imaging malignant melanoma in humans. Unfortunately, the synthesis of IDAB is problematic and, more significantly, IDAB is taken up in high concentrations by non-melanoma cells in the liver and lung. Accordingly, IDAB does not have optimal specificity for melanoma cells and its uptake by non-tumor cells undermines its utility for routine screening of cancer.
U.S. Pat. No. 4,279,887 to Baldwin et al., U.S. Pat. No. 5,154,913 to De Paulis et al. and Murphy et al. (1990 J. Med. Chem. 33:171-178) disclose radioiodonated benzamide compounds for use in imaging the brain only, e.g. .sup.123 I-N-.beta.-phenethyl-o-iodobenzamide or (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-hydroxy-3-iodo-6-methoxybenzamide (IBZM). However, the structure and utility of the compounds disclosed by Baldwin et al., De Paulis et al. and Murphy et al. is distinct from those provide herein.
The present invention provides compounds which bind with high specificity and affinity to the cell surface of cancer cells. These compounds bind, for example, to receptors on the cancer cell surface. One such receptor is a sigma receptor. Sigma receptors are known to be present on neural tissues and certain immortalized neuroblastoma and glioma cell lines (Walker et al. 1990 Pharmacol. Reviews 42: 355-400; and Villner et al. 1992 in Multiple Sigma and PCP Receptor Ligands: Mechanisms for Neuromodulation and Neuroprotection? Kamenka et al., eds. NPP Books, pp 341-353). However, it has been surprisingly found by the present inventors that sigma receptors are prevalent on some types of cancer cells, e.g. neuroblastoma, melanoma, glioma, pheochromocytoma, colon, renal and lung carcinoma cells. Recently, John et al. have found that MCF-7 breast tumor cells express sigma receptors. (1994 J. Med. Chem. 37: 1737-1739). Therefore the compounds of the present invention are useful for detecting and treating tumors, e.g. those containing cells with sigma receptors.
The present compounds are also useful for diagnostic imaging any tissue having a sigma receptor, e.g., a neural tissue such as the brain or spinal cord.